Severe acute respiratory syndrome (hereinafter abbreviated as “SARS”) is an infectious disease that began in Guandong, China in November 2002, and has caused serious infection in nations such as Hong Kong, Taiwan, and Canada. According to the World Health Organization (WHO), the mortality for the patients afflicted with SARS is deduced to be 15% on average, and it is deduced to be 50% or higher in the case of patients aged 65 and over. The SARS coronavirus, which is a pathogenic virus of SARS, is a single-strand RNA virus (see, for example, non-patent document 1). It is known that this virus infects animals other than humans.
Major clinical symptoms of SARS are fever with temperatures of 38° C. or higher and respiratory problems, such as coughing and difficulty of breathing. In some cases, symptoms such as headache, shaking chills, loss of appetite, generalized malaise, diarrhea, or clouding of consciousness are observed. However, these symptoms are almost the same as those of other respiratory diseases, such as influenza. Thus, it is difficult to distinguish SARS from other diseases based solely on its symptoms.
An immunologic procedure has been known as a method of clinical testing. In such testing, the presence of an antibody against a viral antigen in blood, serum, urine, or saliva is inspected. The enzyme-linked immunosorbent assay (ELISA) and the immunofluorescence assay (IFA) are known techniques for detecting antibodies against the SARS coronavirus. With these techniques, however, antibodies cannot be detected at the early stage of the disease. In the case of ELISA, antibodies cannot be detected until 20 days after the development of the disease. In the case of IFA, antibodies cannot be detected until 10 days after the development of the disease (see, for example, non-patent document 2).
Also, a method for detecting antibodies via amplification of the virus gene via PCR has been known. This technique, however, has been problematic since it takes 1 hour or longer for amplification and detection, and the detection sensitivity thereof is low. Accordingly, a method for detecting the SARS coronavirus with rapidity and high sensitivity has been awaited (see, for example, non-patent documents 3 and 4).
The present inventors found that the aforementioned problems could be solved by the LAMP method, which is a method capable of detecting the SARS coronavirus with higher sensitivity and specificity within a shorter period of time compared with conventional techniques, such as immunoassay or PCR. Thus, the present inventors attained the object of the present invention.
[Non-patent Document 1]
The World Health Organization Update 49—SARS case fatality ratio, incubation period, 7 May 2003, Case fatality ratio (date of search: Jun. 24, 2003), URL: http:/www.who.int/csr/sars/archive/2003—05—07a/en/)
[Non-patent Document 2]
SARS: a method of diagnostic assay (Apr. 29, Revision 4-1), date of search: Jun. 24, 2003, URL: http://idsc.nih.gojp/others/urgent/update41-No1.html, the Infectious Disease Surveillance Center (IDSC), the National Institute of Infectious Diseases
[Non-patent Document 3]
Drosten C., et al., New Eng. J. Med., 2003, vol. 348, pp. 1967-1976
[Non-patent Document 4]
“Detection of SARS coronavirus gene via RT-PCR (date of renewal: May 16, 2003), date of search: Jun. 24, 2003, URL: http://idsc.nih.go.jp/others/urgent/update56-b.html, the Laboratory of Influenza Viruses, Department of Virology Iii, the Infectious Disease Surveillance Center (IDSC), the National Institute of Infectious Diseases